Comparison of fluoride release protocols for in-vitro testing of 3 orthodontic adhesives

The objective of this study was to compare the fluoride release of 3 orthodontic adhesives using disks and bracketed teeth with different storage protocols. The adhesives used were a resin-modified glass ionomer (RMGI) (Fuji Ortho LC; GC America, Aslip, Ill), a polyacid-modified composite resin (PMCR)(Assure; Reliance Orthodontic Products, Itasca, Ill), and a composite control, Transbond XT (3M Unitek, Monrovia, Calif). Metal brackets were bonded to the buccal and lingual surfaces of 120 extracted human premolars. Five plastic containers holding 4 teeth (8 brackets) were used for each adhesive protocol. The samples were stored in containers holding 4 mL of deionized water at 37 degrees C for 28 and 84 days for the brackets and disks, respectively. The bracketed samples released larger initial amounts of fluoride compared with the disk samples during the first 5 to 6 days for both fluoride-releasing adhesives. The PMCR (Assure) released more fluoride (mg/cm(2)/day) than did the RMGI (Fuji Ortho LC) in all protocols with the exception of daily protocols when values diminished below the RMGI values near the 24th day and between the 56th and the 70th days for the bracketed and disk samples, respectively. Inconsistent values for fluoride release were noted in the bracket and disk samples when compared with daily versus cumulative water changes. Daily water changes revealed higher fluoride release levels (brackets), but this trend was not evident in the disk samples. Daily water changes may yield more clinically relevant data on fluoride release.